A vehicle engine mixes and burns air, which is injected from the outside, and fuel with an appropriate ratio, thereby generating power.
In the process of generating the power by driving the engine, a desired output and combustion efficiency can be obtained only when fully supplying the external air for combustion. For this reason, in order to enhance combustion efficiency of the engine, as an apparatus that supercharges and supplies air for combustion, a turbocharger is used.
In general, a turbocharger is a device that rotates a turbine using a pressure of an exhaust gas that is discharged from the engine and that enhances an output of the engine by supplying air of a high pressure to a combustion chamber of the engine using a torque thereof. The turbocharger can be applied to both a diesel engine and a gasoline engine.
Further, nitrogen oxide (NOx) that is included in an exhaust gas is regulated as a major air pollution material, and many researches for reducing discharge of such NOx have been performed.
In order to reduce a noxious exhaust gas, an exhaust gas recirculation (EGR) system is mounted in a vehicle. Generally, when combustion is well performed due to a high air ratio in a mixer, NOx increases. Therefore, the EGR system suppresses NOx from occurring by reducing an oxygen amount of the mixer and by disturbing combustion by again mixing a portion (e.g., 5-20%) of an exhaust gas that is discharged from the engine to the mixer.
In order to enhance fuel consumption, the EGR system of a gasoline engine is generally mounted in a vehicle. A pumping loss can be reduced in a low speed/low load area through the EGR system and ignition timing can be advanced by temperature reduction of a combustion chamber in an intermediate speed/intermediate load area, and thus, fuel consumption of the vehicle can be enhanced.
A representative EGR system includes a low pressure exhaust gas recirculation (LP-EGR) apparatus. The LP-EGR apparatus recirculates an exhaust gas, having passed through a turbine of a turbocharger to an intake path of the front end of a compressor.
When the turbocharger operates, a conventional EGR system supplies a recirculation gas to a combustion chamber of an engine by a torque of a turbine and a compressor.
However, when the turbocharger does not operate, a negative pressure scarcely occurs at the front end of the compressor, and thus, a method of applying a separate differential pressure generation valve is reviewed. However, when such a differential pressure generation valve is mounted, a problem occurs that a production cost of a vehicle increases.
Further, a differential pressure sensor that detects a pressure difference between a front end and a rear end of the EGR valve that adjusts a recirculation gas amount is provided, and because a pressure difference between the front end and the rear end of the EGR valve in a low speed/low load area is small, a degree of precision of an EGR control is deteriorated.
Therefore, because an accurate recirculation gas amount cannot be adjusted, combustion stability cannot be secured, and thus, ignition timing cannot be advanced and a problem occurs that it is difficult to enhance fuel consumption of a vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.